While Helicobacter pylori is now established as a pivotal factor in gastric carcinogenesis, its mechanisms of action and timing in the premalignant process are the subject of research. This project builds upon a recently completed 12-year randomized chemoprevention trial in a high-risk region of Colombia. A significantly greater regression of premalignant lesions was observed in study participants who were treated and were cleared of H. pylori infection. Upon completion of the trial, participants who had not been in the ant\-H.pylori treatment arm were offered standard triple therapy. Quarterly contact has been maintained with trial participants, and this project now proposes to evaluate the long-term effectiveness of anti-H.py/or/treatment in an adult population in which the community prevalence of infection is greater than 90%. A cohort of children has been followed-up for 6 years, String tests to culture H. pylori and stool samples to extract DNA are obtained periodically. The specific aims of the study are to: 1. Conduct endoscopy survey, gastric biopsies, and cultures at 18 and 20 years after intervention 2. Test biomarkers of progression of the precancerous process, mainly methylation of CpG islands 3. Genotype Helicobacter pylori at different ages and different stages in the precancerous process RELEVANCE (See instructions): This project provides information of the long term effects of treating patients with antibiotics to cure their infection with the bacterium Helicobacter pylori. The original treatment took place in 1992-1993. How effective the treatment was in preventing cancer development will be investigated.